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Old 09-30-2017, 09:38 PM   #1
Skoolie
 
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5.9 vs. 8.3 fuel economy?

Seems many people say that the 5.9 is bad for power on hills and in mountains... "if you're doing mountains or a lot of highway driving, you want an 8.3"... well, in regular passenger vehicles, a larger engine typically means worse fuel economy.

In a full size bus, roughly what fuel economy difference can you expect between the two engines? (I'm willing to sacrifice top-end highway speed and I'm willing to deal with going 25 up mountain hills if for the rest of my trip I can get good fuel economy. My main mount is a 2014 Prius v... tells you how I feel about giving my money to OPEC.)
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Old 09-30-2017, 09:59 PM   #2
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Honestly probably about the same economy. In fact, the 8.3 might do a little better since it's not working as hard as the 5.9. Diesels by their very nature only use "enough fuel to do the job", as opposed to running at a certain fuel/air mixture as gas engines do.
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Old 10-01-2017, 07:58 AM   #3
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The tranny has a lot to do with it too. A four speed vs. A five and all that....

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Old 10-01-2017, 08:27 AM   #4
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11mpg avg. over 3 years and 10,000 miles. 5.9/545, 3.54 diff, 20,000 lbs. All terrain 55-60 mph.
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Old 10-01-2017, 09:23 AM   #5
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seems i'm always on the low end of mileage threads.... everyone gets better mileage than me.

7.5 mpg, cummins 5.9, ~70mph, at545, 4.7 rear, 21k lbs. ive put 20k miles on it.

go with a an 8.3 or dtt466, they get better mileage than i do.
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Old 10-01-2017, 09:54 AM   #6
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Originally Posted by turf View Post
seems i'm always on the low end of mileage threads.... everyone gets better mileage than me.

7.5 mpg, cummins 5.9, ~70mph, at545, 4.7 rear, 21k lbs. ive put 20k miles on it.

go with a an 8.3 or dtt466, they get better mileage than i do.
I have to agree with Turf.

I have only put a couple thousand miles on my 8.3, md3060,5.38 drive trane and have gotten 9.7-11mpg.
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Old 10-01-2017, 10:40 AM   #7
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You'll probably find the factor that affects your fuel economy more than anything else is how fast you drive. Keep it 55-60 and I would expect somewhere around 10 MPG in a full size bus, regardless of engine size, transmission, and gearing. Push it up to 65 and I would expect mileage to drop to the 8-9 range. Cruise at 70 and watch it drop to the 7-8 range. Bump it up to 75 and expect 6-7 MPG. It takes a lot of fuel to push air out of the way.

Yes, engine size, transmission and gearing *Does* affect mileage, I won't argue that. I drive a Volvo road tractor and average 6 MPG (I generally run 70 on the highways). I have found that if I put the cruise on 62, it will average over 8 MPG.

I drove my bus home from WV at 55 - its top speed. It has a T444 engine and though I have yet to calculate it, I feel like it averaged around 10 MPG.
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Old 10-01-2017, 10:47 AM   #8
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i was pretty curious of mileage and started using an app called "fuel monitor". its handy after a fill up to enter the receipt into the app.

i think for free it tracks one vehicle. i have it on an ipad for the bus and my phone for my daily driver.

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Old 10-01-2017, 11:09 AM   #9
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I don't worry much about speed. I doubt I would ever try to push the limits of a school bus. When I had my Class C, I rarely put it up over 55. If I had to get somewhere quickly, it went to 60, and I only hit 65 once when I wasn't watching the speedometer. The point of having the bus will be to travel all over, hopefully leisurely. If I MUST drive faster than 55, I didn't plan well. (That said, I really don't want a bus that tops out at 55 mph. Surely such a bus would get worse fuel economy at 55 than one that could do 75 but is being driven at 55.)
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